Centralizers or spacers when used with cementable prosthetic implants provide an even spacing between the implant and the supporting bone thus uniformly controlling the thickness of the cement mantle. It is know that such spacers may be formed from polymethylmethacrylate (PMMA).
Numerous types of centralizers or spacers for prosthetic hip stem implants are disclosed in the following:
U S. Pat. No. 4,827,919--Barbarito et al.; PA1 U.S. Pat. No. 4,718,909--Brown; PA1 U.S. Pat. No. 4,549,319--Meyer; PA1 U.S. Pat. No. 4,404,692--Eftekhar; PA1 U.S. Pat. No. 3,793,650--Ling et al.; PA1 U.S. Pat. No. 2,104,391--Lee et al.; and PA1 UK Patent Application 2 216 015--Sheenan. PA1 U.S. Pat. No. 4,538,305--Engelbrecht et al.; PA1 U.S. Pat. No. 4,523,587--Frey; and PA1 U.S. Pat. No. 4,268,920--Engelbrecht et al.
Centralizers or spacers for articulated prostheses used in knees are illustrated in the following:
In general, the centralizers or spacers disclosed above in conjunction with stemmed prosthetic implants require some assembly by the surgeon to connect the spacers to the implant during surgery. Further, the spacers terminate in a blunt trailing edge relative to the leading insertion end of the implant. These blunt trailing edges can cause vortices within the cement as the spacers and implant are inserted into a cement filled intramedullary canal. These vortices can cause voids adjacent the implant when the cement cures. Such voids are generally considered undesirable and may contribute to a weakened connection between the implant and the supporting bone.